1. Field of the Invention
This invention relates to a stopper structure for limiting the range of rotation of a rotary operation member designed to operate, for example, a rotary encoder switch provided in a radio communication device and used to change radio channels. This invention further relates to an electronic device and a channel stopper.
2. Description of the Related Art
Some business-use radio communication devices or portable radio communication devices have rotary encoder switches for changing radio channels. The rotary encoder switches each have a rotational shaft. As the rotational shaft is rotated, the radio channel is changed.
It is known to mount a rotary operation member accessible by a user on the rotational shaft of a rotary encoder switch. As the rotary operation member is rotated by the user, the encoder shaft also is rotated so that the radio channel is changed. Thus, the user can tune the related device to a desired radio channel by actuating the rotary operation member. A typical rotary operation member is designed so that it can be held between user's fingers when being rotated by the user.
Business-use radio communication devices are often used for communications between persons in a building site or persons doing inspection work. It is usual that a user carries a radio communication device on his waist belt. The user often struggles with an operation part (for example, a rotary operation member) of the device on the belt when using the device. Thus, in the case where an excessively large number of selectable radio channels is assigned to one rotary operation member, it tends to be difficult for the user to correctly determine which of the channels is being selected when he actuates the rotary operation member. If the number of selectable radio channels assigned to one rotary operation member is smaller, correct channel section can be more easily implemented.
With respect to a radio communication device on user's waist belt, an example of channel selection performed by the user is as follows. Firstly, the user struggles with the rotary operation member and rotates the member in one direction until the member contacts a fixed stopper provided on the device. Secondly, the user struggles with the rotary operation member and rotates the member in a reverse direction until the device tunes in to a desired radio channel. Sometimes the user would handle the rotary operation member roughly while performing channel selection. Rough handling of the rotary operation member causes a great impact when the member comes into contact with the stopper. Thus, it is desirable that the rotary operation member, the stopper, and the body of the device are strong enough to withstand such a great impact. Furthermore, it is desirable that the rotary operation member, the stopper, and the body of the device are durable.
Japanese patent application publication number 2003-337628 discloses a mechanism for limiting the range of rotation of an operation member (see FIGS. 1 and 2 therein). In FIGS. 1 and 2 of Japanese patent application 2003-337628, the chassis of a radio communication device has an opening through which the rotational shaft of a rotary encoder projects outward. An operation member is mounted on the projecting part of the encoder shaft. As the operation member is rotated, the encoder shaft rotates accordingly. The operation member has an axially-extending projection at a place in its outer circumferential edge. A limiting member formed by a small member is mounted on the chassis for cooperation with the projection of the operation member. Specifically, the inner circumferential edge of the chassis which defines the opening has small recesses spaced circumferentially. The limiting member fits into one of the recesses in a manner such that a portion of the member projects axially from the recess and can contact with the projection of the operation member. The operation member can be rotated until the projection thereof meets the limiting member. The rotation of the operation member is stopped when the projection meets the limiting member. In this way, the rotation of the operation member is limited.
In Japanese patent application 2003-337628, the limiting member is formed by the small member, and tends to have a problem with its strength. The inner circumferential edge of the chassis which defines the opening has a complicated shape so that the chassis is difficult to make.
Japanese patent application 2003-337628 further discloses another mechanism for limiting the range of rotation of an operation member (see FIG. 7 therein). In FIG. 7 of Japanese patent application 2003-337628, a ring-shaped stopper formed by a metal plate and having a stopping projection cooperates with a projection of an operation member. The stopper is fixed to the chassis of a radio communication device by a nut used mainly for attaching the body of a rotary encoder to the chassis. As the thickness of the stopper is smaller, the strength thereof decreases and the stopper tends to more easily bite into the operation member. As the thickness of the stopper is greater, the stopper is more reliably prevented from biting into the operation member. The stopper having a greater thickness however works against the compactness of the radio communication device. To remove the stopper or change the position thereof, it is necessary to loosen the nut through the use of a tool.